1. Field of the Invention
This invention relates to soldering methods and more particularly to a method of effectively soldering components together that have different compositions.
2. Description of the Prior Art
Soldering components that have different compositions presents certain technical challenges. One example of this is the soldering of workpieces made from metal, such as copper, brass, or plated steels, onto glass or ceramic substrates, which may or may not be coated or laminated with a plastic material. Two concerns that arise when soldering different materials together include the different rates of expansion of the materials and the damage that may occur to the substrate, such as the re-crystallization of a silica-based substrate.
Prior art soldering technology requires that the substrate be relatively cool for the heated terminal""s solder interface to solidify. This causes the cooled solder joint to contract and pre-stress the soldered interface, thereby reducing the mechanical strength of the connection. One specific example involves the soldering of copper electrical terminals to the silver oxide painted defrost grid of an automobile""s rear window, as shown in FIG. 1. The rate of expansion for the glass, is approximately 0.000004 inches per degree Fahrenheit, compared to 0.000009 inches per degree Fahrenheit for copper. This becomes a problem when the components are heated and cooled for the solder interface to bond the components together. During heating, the copper terminal will expand more than the glass. During cooling, the solder joint will solidify while the terminal contracts a greater amount than the glass. This causes the fully cooled terminal to exert stress on the solder interface and the glass, reducing the mechanical strength of the connection. This problem is evident in several other applications, including the soldering of electrical connection pins to dense silica monolithic circuit chips.
Prior art soldering methods tend to generate an excessive amount of heat when the heat for soldering is applied. Oftentimes, such soldering methods will generate sufficient heat to damage the substrate. One example of the damage that can be caused is the annealing of tempered safety glass. Safety glass is tempered by first heating it to a critical temperature, then rapidly cooling it below a specific temperature. During the soldering process, the copper terminal is heated to cause the solder to flow, allowing the terminal""s heat to be transferred to the adjacent glass. This becomes a problem when the terminal""s solder temperature reaches or surpasses the annealing temperature of the glass. During cooling, the solder joint will solidify and the glass adjacent to the terminal becomes annealed. This annealed section of the glass will no longer be safety tempered and will no longer break into the small fragments required by Federal Regulations.
Other types of damage to the substrate may include the melting or disfiguring of plastic materials and laminates. Such materials are also susceptible to discoloration or, in the case of a transparent substrate, rendering the substrate opaque. Unfortunately, those of skill in the art are well accustomed to these and other types of damage that occur to substrates during a soldering operation.
The damage that can occur during a soldering operation is not limited only to the substrate. There may be instances where the heat generated by the soldering operation is transferred to an adjacent component coupled to the substrate. There may also be instances where a workpiece is provided with a circuit or other such sensitive component coupled thereto. Excessive heat transfer during a soldering operation frequently results in the damage of such components, which may not become apparent until it is too late.
Therefore, there is a need for an improved method and system for soldering components together that are composed of different materials.
A method and system for rapidly soldering a workpiece to a substrate, having a different material composition than the workpiece, is disclosed herein. The system comprises an intense heat source, such as an intermittent micro flame, a workpiece gripper, having gripping jaws that are comprised of a heat-conductive material, and an optional air-jet cooler.
The workpiece is first secured between the jaws of the gripper, which are further adapted to selectively position the workpiece closely adjacent a point of use on the substrate. Intense heat is applied to the workpiece, in this instance being coated with a solderable material, causing the solderable material to melt. The jaws are sufficient in thermal conductivity to serve as a heat sink, preventing the temperature of the workpiece to significantly increase beyond the melting point of the solderable material during heating. This minimizes the transmission of heat from the workpiece and layer of molten solderable material to the substrate. After the solder has melted, the intense heat source is shut off and an optional jet of cool air is directed to the workpiece. While the jet of air is cooling the workpiece and layer of solderable material, the gripping jaws continue to remove residual heat from the workpiece. These methods of cooling cause the solder joint to rapidly solidify.
Using this method and system, the time required to first melt the layer of solderable material and then solidify the solder connection is short enough that the effect of the different rates of expansion between the workpiece and the substrate is greatly minimized. This is of great importance when the workpiece-receiving substrate is made of glass, such as tempered safety glass or other material that is easily damaged during the soldering phase. The rapid heating and cooling time aid in preventing damage to the substrate and further allows for a stronger solder joint.
Therefore, a principal object of the invention is to provide an improved system for rapid heat sink soldering.
A further another object of the present invention is to provide a system for rapid heat sink soldering that reduces the heat transfer from a heated workpiece to a substrate.
Still another object of the invention is to provide a system for rapid heat sink soldering that reduces the time required for solidifying the layer of molten solderable material.
Yet another object of the invention is to provide a system for rapid heat sink soldering that will not damage the substrate to which a workpiece is soldered.
A further object of the present invention is to provide a system for rapid heat-sink soldering that will not damage components coupled to a workpiece when the system is used to solder the workpiece to a substrate.
Still another object of the invention is to provide a system for rapid heat sink soldering that minimizes the effect of the difference in the rate of expansion between a workpiece and a substrate of different compositions when the two structures are soldered together.
These and other objects will be apparent to those skilled in the art.